37G THE PENOKEE IKON-BEAEING SERIES. 



The proportion.s lit" these minerals vary widely in the ditiferent sections. In 

 one variety a quartzose backgToun<l sul)ordinate in quantit}' contains fine 

 debris from the l)asic eruptives; that is, tabular plagioclases, actinolite, 

 and chlorite, all of the minerals being- mingled in the most confused miinner, 

 but generally showing a laminated structure. In another variet}' of frag- 

 mental matrix of about equal importance to the last the background is 

 composed almost wholly of (juite pure finely crystalline and chalcedonic 

 quartz, in which are well outlined sharp areas of intermingled chlorite and 

 epidote. Between these two main varieties there are various gradations. 

 In some of the sections the matrix and fine fragmental material have a 

 pretty well defined stratiform arrangement; in others, they vary from this 

 regular stratiform character to a most extraordinary irregular arrangement, 

 the fragments being extremely angular, and the matrix between ruiming 

 around and through them in the most lawless fashion. Words fail to gi\e 

 any proper conception of this sti'ange appearance, but some idea of it will 

 be obtained by reference to PI. xxxv. Figs. 2, 3, and 4. Of less impor- 

 tance than the foregoing are the l)lack chlorite-slates and black calcareous 

 slates. These phases are usualh* nonconglomeratic, and are precisely like 

 the slates of the fragmental l)elt north and east of the greenstone-conglom- 

 erates. Some of them contain unmistakal)le fragmental quartz mingled 

 with fine grained cla^'ev material. C)thers contain a g'ood deal of some 

 carbonate, oxides of iron, and finely crystalline (juartz ; in other words, are 

 like the mingled nonfragmental and fragmental water-deposited sediments 

 of the eastern area. 



The fragments of the conglomerates vary from large liowlilers to 

 'single individuals of one mineral. The pebbles are usually numerous, and 

 often so thickly set as to give little room for a matrix, although they vary 

 in abundance and are sometimes absent. It has already been stated that 

 the great majority of the pebbles are of two well defined tvpes. The com- 

 mon light green or grayish-green pebbles are ordinaril}' fine graiiu'd to 

 aphanitic porphyrites, which are (piite often amygdaloidal. Their liack- 

 grotnid varies from glassy to holocrystalline. When glassy, tln'v have 

 been almost \vlioll\- devitritied, being changed into a pale green or light gray 

 nonpolarizing or very feebly polarizing aggregate. The common recog- 



